1. Field of the Invention
The present invention relates to an autofocus technology that automatically adjusts the focused state of a subject in an imaging apparatus.
2. Description of Related Art
The imaging apparatuses such as a digital still camera and a digital video camera which has an image sensor, for example a CCD (Charge Coupled Device) sensor and a CMOS (Complementary Metal Oxide Semiconductor) sensor, have been input into practical use. As the autofocus (AF) method applied to these imaging apparatus, the contrast detection method which uses through-the-lens images obtained by the image sensor is known.
The contrast detection method uses that the contrast of the through-the-lens image obtained by the image sensor increases if the subject image formed by the imaging optical system on the imaging surface is focused.
Specifically, by moving the position of the focus lens or the image sensor included in the imaging optical system, and sequentially changing the imaging position of the subject image, the through-the-lens images are sequentially obtained. Then, the contrasts of multiple through-the-lens images sequentially obtained by the image sensor are obtained, and the imaging position of the subject image where the contrasts reach their maximum is determined as the focal position.
The integrated value of the high frequency component in the spatial frequency is used for the contrasts, for example. In the continuous AF, the position of the focus lens where the contrast of the through-the-lens images reaches its peak is searched while driving the focus lens by step.
Further, there is a known imaging apparatus for performing the face detection process that detects the image of a person's face included in the shooting screen obtained by the image sensor, and the focusing control in order to focus on the detected face image (Japanese Unexamined Patent Application Publication No. 2007-34261 (Sugimoto)).
In the technique disclosed by Sugimoto, as illustrated in FIG. 9, in a case of the continuous'AF (YES in the step 35), the focusing range which is to be the moving range of the focus lens in the usual search process is determined using the result of the continuous AF (step 36). Then the focus lens is moved within the determined focusing range, and the usual search is performed.
FIG. 10 illustrates the result of the continuous AF (upper side), and the usual search operation (lower side) in the technique disclosed by Sugimoto. As illustrated in the upper side of FIG. 10, by performing the continuous AF using the through-the-lens image data, it is possible to obtain a position Z12 of the focus lens when the through-the-lens image is focused. The range between the distance a on the NEAR side away from the position Z12 of the focus lens and the to distance b on the INF side from the position Z12 is determined as a focusing range (Z11 to Z13).
Japanese Unexamined Patent Application Publication No. 2003-348426 (Aoki) discloses that when a shutter button is pressed during the continuous AF, the operation of the usual search afterward is determined depending on the operation in the continuous AF. If the shutter button pressed state is in the finely adjustment of the focus lens position or movement of the focus lens to the focused position corresponding to the peak position, in the usual search, the search is performed in the range of the current position or the peak position. Further, in the state of moving the focus lens and searching for the peak position, the usual search is performed from the current position of the focus lens toward the current driving direction.